It has been a standard practice for many years to apply to carpets and upholstery, mainly those made of nylon and other natural and synthetic polyamides, fluorocarbon finishes. The purpose of such finishes is to protect the said substrates, frequently used and expensive to clean, from oil and water-borne soils.
Fluorocarbon finishes, among which there are brands such as Scotchgard (by 3M Company), Zepel, and Teflon (the latter two are by E. I. du Pont de Nemours & Co.), offer oil and water repellency to substrates finished with them, and thus also protect against soils, both oily or aqueous in nature.
Although fluorocarbon finishes do perform their intended functions, they have one important drawback. When a droplet of oil is deposited on the surface of a fluorocarbon-treated substrate (or a droplet of water), it does not soak into the substrate, but stays on the surface forming a bead. If however, this bead is pressed, with a hand (or a shoe, in the case of carpets), the oil or water bead will penetrate the fabric.
The above described phenomenon is not of great concern when the liquid medium is not a soil carrier, i.e. clean medium; but if the medium is contaminated, the substrate will soil.
Such soiling, especially if its sources are oily foods or aqueous drinks, colored with artificial colorants, will, especially on polyamide substrates (i.e. nylon, wool), leave a visible spot, often indelible. The reason for this is that said colorants are anionic dyes of the same class used to dye nylon and wool. In addition, many foods, and especially drinks, contain acids which accelerate the dyeing process of polyamides; that is, such dyeing can proceed at room temperature in the presence of citric, tartaric, and other acids used in the preparation of edible and potable products.
Moreover, practically all fluorocarbon finishes, such as Scotchgard FC-352, FC-358, FC-393, specifically intended for carpets (called "carpet protectors" by the manufacturer) are fluorocarbon emulsions prepared with a cationic emulsifying system. This aggravates the problem, described in the previous paragraph, as follows:
Since the food colors, described above, are anionic in nature, they will be attracted to substrates finished with the said fluorocarbons, unless the cationic emulsifier is completely removed from the carpet by rinsing after finishing. This is not easy because, at this point, the finished substrate is water repellent and the rinsing medium can not penetrate the substrate to remove said cationic emulsifier. This problem can be overcome, as will be seen further below.
Because of the above described drawback, coupled with frequent incidents involving spilled foods and soft drinks containing food colors, the carpet fiber manufacturers developed new carpet protection systems, such as Stainmaster.TM. (E. I. du Pont de Nemours & Co.). This and other systems involve the application of a stainblocker (acid dye reserving agent) usually before applying the fluorocarbon finish. In some cases the fluorocarbon finish is built into the fiber before the substrate (i.e. carpet) is made. In such cases, the stainblocker application follows in the dyeing establishment.
Such stainblockers have been described in U.S. Pat. Nos. 4,501,591; 4,592,940; and 4,680,212.
This sequential application of stainblocker and fluorocarbon finishes came to be known as "total stain protection" in the consumer market.
At this time the carpet mills are willing to accept the extra step required to accomplish this "total stain protection" because of the good consumer reception of this new development. However, if it were possible to apply the said fluorocarbon finish together with the stain blocker, that is in a one-bath-one step fashion, the mills would realize considerable labor and time savings. Moreover, since all finishes affect the cast of a dyed shade, which must be compensated for when developing a dyeing formula, a one-step procedure would simplify this compensation, i.e. a single compensation is quicker to accomplish than a double one. Even in the case of fibers with built-in fluorocarbon finish, the mills are often forced to fortify their effect with a topical application of more fluorocarbon in the mill, so that in practical terms, "the total stain protection" is almost always a two-step process.
There is another important area where a one-step process would be desirable. There arises a need to apply fluorocarbon and stain blocking finishes on carpets already installed in private homes or institutional buildings, such as hotels, offices, hospitals, etc. to, boost the effect of mill-applied finishes following professional cleaning operations (which decrease the "total stain protection" effect after a number of such cleanings). Such "on-site" applications are also carried out on older carpets which lack such "total stain protection."
At this time such on-site finishing must also be carried out in two steps, as in the mills, with the ensuing aggravation to the private home owners and the institutional patrons because the premises can not be used while the carpet is treated, and while it dries. Hence a one-step process would be very desirable in this case as well.
It is known, that stainblocking agents are all strongly anionic compositions (see the above mentioned patents) and the fluorocarbons, mentioned above, are emulsions containing cationic emulsifiers, thus, when combined in a single bath they precipitate due to mutual neutralization of the cationic and anionic charges of the respective finishes. There are, however, a few fluorocarbon finishes that are nonionic in nature, such as Scotchgard FC-357. However, products such as he latter are emulsions, or dispersions, (some companies describe them as emulsions, others as dispersions) and are very sensitive to anionically charged compounds, such as stain blockers. These said emulsions or dispersions are broken when they are put in contact with the said stainblockers.
There exist very few solution-type nonionic fluorocarbon finishes, such as the Fluorinated Esters Enumerated in U.S. Pat. No. 4, 472,466. These products, although described by the manufacturer as a "fluorochemical emulsion", are actually quasi-solutions at the specific concentrations offered for sale. These products should in theory be compatible with stainblockers, such as those described in U.S Pat. Nos. 4,501,591; 4,592,940; and 4,640,212. Unfortunately, this is not the case. Fluorinated Esters are acid in nature (pH 3.2), whereas the stainblocking finishes have a pH above 7, or as high as 10. When the latter fluorocarbon finish is mixed with stain blocking finishes, such as those of the prior art, a precipitate settles to the bottom of the combined solution. The same phenomenon occurs when attempting to equalize the pH of both products by raising the pH of the acid finish, or by lowering the pH of the alkaline finish, with base or acid, whatever the case may be.